It has long been known that isobutylene can be polymerized into high molecular weight liquid polymers by the use of Lewis acid catalyst such as aluminum chloride. In the process, isobutylene, or isobutylene and butenes, or a mixture of C.sub.4 olefins as isobutylene in the presence of other butenes or a "BB" stream comprising isobutylene, other butenes and butanes, is passed through a reactor in the presence of AlCl.sub.3 catalyst at a temperature within the range of from about 0.degree. F. to about 100.degree. F. at a pressure sufficient to maintain the contents of the reactor in a liquid state. Usually the pressure is within the range of from about 7 psi to about 50 psi. The extent of polymerization is controlled by regulating the amount of catalyst introduced into the reactor, said amount being in the range of about 0.005 to about 1 weight percent, preferably about 0.05 to about 0.2 weight percent based on the amount of fresh isobutylene-butenes charged. The AlCl.sub.3 is preferably introduced as a slurry about 5 to 10 wt % in hexane or other dispersing medium to obtain uniform contacting thereof with the undiluted olefin stream. The amount of AlCl.sub.3 is preferably limited to obtain 80 to 90 percent conversion in an isothermal stirred tank reactor.
In the event of reaction malfunction, as for example, wherein catalyst is added to the reactor in excess of operational requirements, or temperature and pressure become excessive, since the polymerization reaction is exothermic, an explosive condition can readily occur. An immediate shutdown of the reaction is required to prevent a "run-away" butylene polymerization reaction since its reaction rate increases with temperature.
As an example, most commercial butylene polymerization processes to produce polybutene use solid AlCl.sub.3 as catalyst. The heat of the exothermic polymerization reaction is typically removed with a refrigeration system. If for any reason the AlCl.sub.3 catalyst is more active than conditions require, the heat generated can exceed the capacity of the cooling system. The temperature of the reactor content will rise. The rise in temperature accelerates the reaction and generates more heat. The "run-away" reaction is very dangerous and can result in explosion of the reactor.
Methods of terminating a butylene polymerization reaction have been described in the prior art. U.S. Pat. No. 2,918,508 teaches, in a recycle reaction to produce polyisobutylene, the reactor effluent is diluted with incoming isobutylene to avoid polymerization at an unduly high temperature and a molar excess of ammonia is added to the reactor effluent which is not recycled to further quench the reaction.
The method to terminate a butylene polymerization by dilution is suitable for use in a plug flow reactor where conversion per pass is low. In a stirred tank reactor, additional feed would increase the rate of polymerization. Addition of ammonia can aid in a liquid full reactor without liquid and vapor phases. In a boiling reactor with a liquid phase and a vapor phase, any gaseous agent, such as ammonia, added to the reaction to quench the reaction, would tend to boil up into the vapor phase, and react very little with the solid catalyst which remains in the liquid phase.
U.S. Pat. No. 2,628,991 teaches the elimination of catalytic activity from a gaseous stream containing reactive olefin hydrocarbons, such as isobutylene, wherein the catalyst is boron fluoride, BF.sub.3, by means of the addition of low boiling dialkyl ether, preferably diethyl ether. The diethyl ether when dispersed into the gaseous olefin stream, particularly with some of the ether in the gaseous phase, acts very rapidly, even at low temperatures, to form a complex with the BF.sub.3 and thus prevents undesired reaction of the reactive hydrocarbon. The gaseous olefin stream containing the BF.sub.3 catalyst can also be reacted with the ether in contact with a nonvolatile oil slurry of sodium fluoride. The presence of the ether causes the BF.sub.3 to react rapidly with the sodium fluoride to form a solid complex sodium fluoroborate, NaBF.sub.4. However, in a stirred reactor with liquid and vapor phases and solid catalyst, use of a dialkyl ether, such as diethyl ether, with its low boiling point, is unsatisfactory. The ether escapes into the vapor phase and reacts little with solid catalyst in the liquid phase.
U.S. Pat. No. 2,521,940 teaches a method for removal of catalyst from the polymerization reaction effluent and polymer product in the polymerization of olefins wherein the reaction is catalyzed with a metal halide catalyst and promoted with a hydrogen halide catalyst promoter. Effluent from the reaction zone is admixed with alcohol to react with the metal halide catalyst to form an alcohol-metal halide complex which is insoluble in the effluent. The effluent is then contacted with water to dissolve the hydrogen halide promoter and reconvert the complex to the alcohol. U.S. Pat. No. 2,965,691 also teaches the use of a polar compound such as methanol to deactivate the catalyst system. U.S. Pat. No. 3,156,736 teaches deactivation of the catalyst by washing with an alcohol, water or other suitable material.
Water and alcohols require vigorous mixing to be dispersed rapidly in a butylene polymerization reaction to terminate the reaction. Vigorous mixing may not be available in an emergency. Also, water and alcohols, in concentrations of 20 to 100 ppm can act as promoters and accelerate the "run-away" reaction.
A run-away reaction can be handled by venting the reactor content with a pressure relief valve. However, the vent system must be very large to be effective to contain a run-away reaction. A rupture disk, or number of rupture disks, can be utilized. But a sufficiently large vent system can be uneconomical and use of rupture disks requires process downtime to replace the disks if the disks rupture.
Acetonitrile (ACN) has been proposed as a fast-acting emergency catalyst deactivator to deactivate Lewis acid-type catalysts in olefin polymerization reactions. Acetonitrile is highly toxic, both as the material and its combustion products. Water, alcohols, anhydrous ammonia nitriles, and other catalyst deactivators taught in the prior art can act as strong promoters and can accelerate the reaction when added in small amounts. The amount required of these agents to deactivate AlCl.sub.3 catalyst is about 1:1 upon a molar basis. Insufficient addition of these agents can accelerate the reaction.
Despite the well-known methods of deactivating the Lewis acid-type catalyst used for polymerizing olefinic feedstocks, as evidenced by the above prior art, the termination of a run-away olefin polymerization reaction in a time period no greater than seconds has not been addressed wherein the deactivation is accomplished in a safe, expeditious and convenient manner.
Polymerization reactions of olefins to which the instant invention is applied include the polymerization of 1-butene to poly-1-butene in the presence of a promoter such as a chloride and a Lewis acid-type catalyst, the polymerization of isobutylene to polyisobutylene in the presence of a Lewis acid-type catalyst, the polymerization of propylene to polypropene in the presence of a Lewis acid-type catalyst, and the polymerization of alphamethylstyrene to poly-alphamethylstyrene in the presence of a Lewis acid-type catalyst.
It is therefore an object of this invention to provide a method for rapidly deactivating the above polymerization reactions in the presence of a Lewis acid-type catalyst within a time period of 30 seconds or less when reaction pressure approaches pre-set limits based on equipment design factors. Although these pre-determined pressures can be of any suitable value, maximum pressures initiating reaction termination are typically less than 250 psig as equipment designed for higher pressures would be uneconomical under normal process conditions.
It is an object of this invention to provide a process for deactivating a run-away olefin polymerization reaction wherein the reaction is killed almost instantaneously, that is, within a period of 30 seconds or less. It is further an object of this invention to utilize a reaction kill-agent which is non-toxic, is completely miscible with hydrocarbon solvent so that it can be easily dispersed in the reactor, is very high boiling so that it is not easily lost via the vent system, is not a promoter for olefin polymerization, forms a complex with Lewis acid-type catalysts with very little liberation of heat, is soluble in water, and is easily removable from the reactor products after the reaction is killed.
It is an object of this invention to provide a method for termination of a polymerization reaction of a reactive olefin under emergency conditions wherein said reaction is catalyzed with a Lewis acid-type catalyst, the reactor is a stirred, boiling-type reactor, reactor contents comprise a liquid phase and a vapor phase, and the method of termination does not involve a toxic substance.
It is further an object of this invention to provide a process for deactivating Lewis acid-type catalyzed olefin polymerizations wherein AlCl.sub.3, or BF.sub.3 or complexes of BF.sub.3 are the catalysts. Other Lewis acid-type catalysts can be used such as aluminum bromide.
Surprisingly, it has been found that diglyme, diethylene glygol dimethyl ether, forms a complex rapidly with Lewis acid-type catalysts and effectively terminates catalytic activity within seconds of contact with the catalyst. Since diglyme does not act as a promoter, addition of insufficient diglyme does not accelerate the reaction, as do water, alcohol, and other deactivating agents. Addition of insufficient diglyme means a less efficient deactivation. Diglyme is not toxic.